Method of producing viscose



2,979,500 Patented Apr. 11, 1961 Unitedstates Patent 2,979,500 METHOD onPRODUCING vrscosE' Fritz Opderbeck, Okriftel (Main), Bonnemuhle,Germany; and Giinther Trapp and Giinter Wiirner, both of Okriftel(Main), Germany, assignors to Phrix Werke Aktiengesellschaft, Hamburg,Germany No Drawing. Filed May 13, 1958, Ser. No. 734,824

9 Claims. (Cl. 260-217) The present invention relates to an improvedmethod of producing viscose, and more particularly to a method ofproducing viscose which permits the omission of the ageing step whichwas always considered essential.

In the known methods of producing viscose wherein the cellulose issteeped in caustic soda solution, pressed and subsequently shredded, thesoda cellulose is subjected to an ageing step requiring about one tothree days. During this time, in which the soda cellulose is in generalsubjected to somewhat increased temperature and the action ofatmospheric oxygen, a depolymerization of the cellulose occurs whichmakesit possible to obtain a viscose of desired spinning viscosity afterthe xanthation, utilizing the usual cellulose content of about 8%. Ifthe ageing step is omitted in the production of viscose, then in themaking of solutions of the usual cellulose content the solutions areextraordinarily thickly liquid and highly viscous and by normal meanscannot be pumped through the spinning pump, and most important cannot befiltered.

The carrying out of the ageing, which for the reasons given above hasalways been an essential stage in the production of viscose, requiredthe installation of large storage rooms and apparatus in order to takeup the soda cellulose production for the necessary ageing time. Thisresults in a considerable loss in total capital. Attempts to acceleratethe ageing by the addition of chemicals to It is another object of thepersent invention to provide a method of producing viscose wherein thesoda cellulose can be directly, after shredding, subjected to xanthationstage without the need for an intermediate ageing stage, and wherein thesubsequent spinning and filtering of the cellulose solution is notinterferred with.

Furthermore, in accordance with the object of the present invention thefinally produced viscose fibers have the properties which are at leastequivalent to the properties of viscose produced in the normal, moreexpensive manner, in which ageing was utilized.

' It is yet a further object of the present invention to provide amethod of producing viscose starting from enzymatically digestedcellulose whereby it is possible to completely omit the ageing step inthe production of the viscose and whereby the resulting viscose fibershave properties at least equal to the properties of viscose fibersproduced in the normal manner.

- Other objects and advantagesof the present invention will be apparentfrom a further reading of the specification and of the appended claims.

With the above objects in view, the present invention mainly comprises amethod of producing viscose in which enzymatically digested cellulose isconverted to viscose.

'It has been found that by the action of a cellulosedigesting enzyme oncellulose before the cellulose is subjected to the stages in theproduction of viscose, it is possible to control with absolute certaintythe desired degree of polymerization of the cellulose which goes intothe formation of the viscose so that it is possible to completely omitthe ageing step in the production of the viscose. By proceeding in thismanner, namely subjectingcellulose to enzymatic digestion by means of acellulose-digesting enzyme, it is possible to maintain a degree ofdecomposition within the desired ranges. Cellulose treated in thismanner can be quickly worked up to solutions of the usual concentrationand can be spun in the usual spinning bath into fibers of markedhomogeneity. The fibers produced in this manner are in no way inferiorto viscose fibers produced according to the classical methods. Althoughcellulose has been decomposed by enezyme prior to the present invention,the use of such cellulose in the production of viscose was unknown priorto the present invention, and it was completely unexpected that by theuse. of such enzymati' cally digested cellulose it would be possible tocompletely avoid the ageing step in the production of viscose.-

. The digestion of the cellulose by means of the cellulose-digestingenzyme is preferably carried outafter prior milling or other mechanicalor chemical pretreatments of the cellulose, wherein for example alkalisor acids maybe utilized. The action of the cellulose advantageouslytakes place at somewhat increased temperature, for example about 30 C.It is particularly advantageous to utilize for the digestioncellulase-preparations which are obtained from cultures of Aspergillusoryzae or Aspergillus niger. It is most advantageous to carry out thistreatment utilizing relatively low pulp consistency, for example in themill hollander. The pH-value of the solution is preferably maintained inneutral or acid range,

for example at values between 3 and 6. In this manner it is possiblewithin an hour to already lower the Cuoxamviscosity of the cellulose,measured according to standard methods, from 21.6 to 11.1.

It is most advantageous to carry out the digestion of the cellulose bymeans of the enzyme in order to lower the degree of polymerization ofthe cellulose in the following manner:

In order to accelerate the action of the enezyme prep,"- aration on thestarting material the bio-structure-of the source of cellulose is firststructurally changed by mechanically opening the same. This can forexample be carried out by milling or other mechanical comminutingdevices. It is particularly advantageous to wet mill the substance in ahollander. Since the greater the degree of opening of the startingmaterial the greater the acceleration of the enzymatic digestion, it isadvantageous to carry out the milling until a milling degree of about 50SR (Schopper-Riegler), and most preferably to a still higher millingdegree of 70 or SR utilizing a crushing milling. By milling in thismanner the degree of polymerization of the starting material is even notat all or only to very slightest degree lowered. Thus, utilizing astarting material having a degree of polymerization of 720,corresponding to a Cuoxam-viscosity of 21.9 cp., and subjecting thisstarting material to milling up to a millingdegree of 70' SR, the degreeof polymerization of the resulting cellulose is 690, corresponding to aviscosity of 20.6 cp. However, the milling in this manner has the efiectof greatly accelerating the subsequent action of the enzyme preparation,

It is possible to carry out the milling and the enzymatic digestion in asingle procedure. advantageous since under certain circumstances a localoverheating of the reaction solution in the mill might occur which wouldhave a deleterious action on the strength of the enzymatic preparation.

The decomposition by means of the enzyme is preferably carried out inthe region of the optimum action of the enzyme. Tests have shown thatcellulase-containing enzyme preparations still act rather slowly at C.;the optimum appears to be about C., While further warming of thereaction mixture to about C. results in a slowing of the action of thepreparation, and furthermore starts deleterious action on the enzymepreparation.

A great number of organisms are known which have the ability to formcellulase-containing enzyme preparations. In most cases however theisolation of a cellulaserich enzyme preparation from these organisms fortechnical purposes involve considerable difficulties because of thecontent of other bacteria in the preparations. For large scale technicalpurposes for the production of the necessary cellulase-containingpreparations, it is suitable to utilize various fungi which, ifnecessary by repeated breeding in the presence of cellulose are broughtto a condition wherein the same form large amounts of cellulase. Forlarge scale carrying out of the process it is possible for exampleutilizing the principle of surface culturing on wheat bran with theaddition of cellulose to utilize cultures originating from Aspergillusoryzae. Milling in the presence of water frees the enzyme and destroysother substances and the cellulase dissolved in water is separated fromthe nutrient medium by filtration. In similar manner it is possible toproduce suitable cellulase-containing enzyme preparations starting fromother materials. The culturing can be carried out as surface culturingor submersed culturing. Among the other suitable bacteria that may beused are Myrotheciom veriucaria, Lancites sepiaris, thermal-bacteria andprotozoae. In addition use can be made of natural cellulase sources suchas vineyard snails.

The concentration of the enzyme in the solution can be maintained withinrather wide ranges.

For example, experiments were carried out in such a manner that 100grams of dry substance of the nutrient were dispersed in 1 liter of tapwater and 250 cc. of the filtered extract applied to 10 grams ofcellulose. It was found that even by applying an enzyme solution dilutedto one half or even to a quarter of the above concentration, the speedof breaking down of the cellulose was not weakened to such an extentthat such diluted solutions could not be used successfully for carryingout the present method.

The pI-I-value of enzyme solutions obtained as described is generallyabout 6.0. It is particularly advantageous to use the solution at a pHof between 4.0 and 6.0 for the splitting of cellulose.

The enzyme solution after being used once can be repeatedly reused afterseparation of the cellulose which was broken down in the desired manner,without giving rise to any noticeable reduction of the depolymerizingpower of the enzymes (except for losses due to adsorption on thecellulose).

This is somewhat less chains, so that a considerable unification(equalization) of the degree of polymerization of the material isachieved. This is of particular advantage for the further treatment ofthe cellulose, particularly for the forming of cellulose solutions suchas viscose, copper oxide ammonia solutions, or for the preparation ofcellulose esters and others.

The fact that the longer chains are subjected to the preferred attack bythe enzyme, is established by examination of the solubility of thematerial in sodium hydroxide of varying concentration. The experimentshows that the amount of the cellulose fractions which are soluble in 2%and 6% sodium hydroxide remains substantially unchanged even upon enzymeattack of prolonged duration. However, the amount of cellulose fractionssoluble in l0% sodium hydroxide, corresponding to a degree ofpolymerization of between 400 and 500 rises continuously during theentire course of the enzyme treatment. This means that the short chaincellulose fractions which are soluble in dilute lye are practically notincreased by the enzyme attack, while in contrast thereto a continuousincrease in the quantity of cellulose fractions which in 10% lye arejust still soluble and which correspond to medium chain lengths, occursunder the influence of the enzyme. A polydispersion diagram of fractionsof the enzymatic treated cellulose which were separated by their chainlengths and transformed into their nitrates also shows a maximum at adegree of polymerization of be tween 400 and 600.

It is probably of particular importance that the yield of cellulose ofreduced degree of polymerization obtained according to the method evenupon subjecting the cellulose to the action of the enzyme preparationfor many hours, amounts upon optimum conditions to 100%. Thus, themethod does not cause any losses of starting material. That in fact thetreated cellulose is not damaged by the new method but is only subjectedto an evening out of the chain lengths is determined by determination ofthe copper number of the treated cellulose which represents its reducingability. The copper number rises only during the first hour of theenzymatic splitting digestion by only a very small amount and remainsthereafter, however, within certain margins of errors, constant duringthe entire length of the treatment. This proves that reducing sugars,particularly glucose are not formed by the method. This at firstsurprising fact can probably be explained in that by carrying out thenew method as described, any cellobiase which may be present in theenzyme preparation and which would cause splitting of the material intosimple sugars, can only become active after the starting material hasbeen broken down to dior trisaccharides. However, before this state isreached, any cellobiase which may be present in the enzymatic extract isalready weakened to such an extent that it can on longer cause anyrecognizable effect.

Drying of the treated cellulose under ordinary condi tions results in astrongly horny material, the reactivity of which-due to its compactsurface structure, is lower than desired. For this reason, it isrecommended to By treating cellulose with the mentioned enzymepreparation, it is possible under the described conditions to achievewithin a few hours a breaking down of cellulose to a considerablyreduced degree of polymerization. Under favorable conditions, it ispossible, for instance, to reduce the viscosity of a cellulose withinone hour from 21.6 to 11.1 cp., corresponding to a reduction in degreeof polymerization from 720 to 470. Thereby, the breakdown first occursfast and slows down during the further course of the same.

Surprisingly, the breakdown of the cellulose chains does not occurhaphazardly, to the contrary, the enzyme causes the preferred splittingof the longer molecule carry out the drying by replacing the watercontained in the final product with organic solvents. For instance, thedrying of material obtained in the above way can be carried out in sucha manner that the treated cellulose is freed of Water with methanol orethanol and that the alcohol-containing material is further washed withbenzene, pyridine or similar solvents for replacement of the alcohol. Inthis manner hornification of the material during drying of the same canbe excluded to the greatest extent while its reactivity, increased bythe inclusion of hydrophobic organic substances, remains intact.

In any event, it is recommended to thoroughly wash cellulose which hasbeen treated as above prior to drying n lq tg f. t m rins due he. messae of the enzymes further breaking down of the material during storagecould occur.

Furthermore, such material when containing remnants of the enzymesolution obviously tends to mold formation; By' short heating or bytreating with. a fungicide,

it is possible, however, to stabilize the material in a simple manner.

The following examples which are taken from a large number ofexperiments will illustrate the method.

Example I 5 Degree of polymerization 690 Cp. 20.6 Copper number 1.59

100 grams drylsubstance of the thus obtained material are now treatedwith 2.5 liters of an enzymatic extract at a temperature of 30 C. Theextract is obtained as follows: v

A strain of Aspergillus oryzae is cultivated on a nutrient consisting ofwheat chafl? and cellulose until a dense mass of mold is formed. Theentire material is then milled in a hollander for one half hour withtimes its quantity of tap water (calculated relativeto the dry nutrient)and thereafter filtered through kieselguhr. The thus obtained solutionshows slight colloidal turbidity. v

The treatment of the beaten cellulose with this enzyme solution iscarried out at 30 C. and at a pH of the solution of 5.2, which pH dropsduring the treatment to 4.1. A sample of the cellulose taken after 2hours shows the degree of polymerization of 445 corresponding to a cp.of 9.8. The copper number rises to 2.22. After 5 hours the degree ofpolymerization drops to 385, corresponding to a cp.-value of 8.2, thecopper number still amounts to 2.22.

Example I! The starting material is beaten in the same manner asdescribed in Example I. The treatment, however, is carried out with anenzyme solution diluted to half the strength of the enzyme solutionaccording to Example I. All other conditions are similar to those inExample I. After 5 hours a degree of polymerization of 480 is foundcorresponding to a cp.-value of 9.9, a repeated dilution of the enzymesolution to half its strength results after 5 hours in a degree ofpolymerization of 525, corresponding a cp.-value of 12.8.

Example III The depolymerization is carried out as described in ExampleI, however, the temperature of the solution is kept at 20 C. After 5hours the degree of polymerization of the thus treated cellulose is 455,corresponding to a cp.-value of 10.0.

Example IV A fir-paper-cellulose which was reduced in a stone hollanderto a fineness of 70 SR is used as starting material.

The starting material is evenly distributed in fungus extract so thatthe concentration of starting material dry substance, amounts. to 2.5grams per liter of fungus extract. Thereafter, a sheet is formed on thesheet-forming apparatus according to Schopper-Riegler. The still moistfiber felt is couched onto'a carrier cardboard and is stored in moistcondition (dry substance 15-20%) for 2, 4, 5 and 8 hours at 20 C.

The fungus extract is formed by grinding 4000 grams fungus culture fromAspergillus oryzae on wheat chaff, in 40 liters water and filtering theaqueous extract through kieselguhr. 1 liter of the thus obtainedenzymescontaining solution is used as described above for forming of thesheet.

In these experiments, the concentration of the enzyme in the cellulosepulp is small, since at a dry substance content of the sheet of about20% the relationship of material to liquid is the same 1:4. 7 After theprovided reaction time, the moist sheets are dried at 96 C. for 6minutes in order to interrupt the depolymerization reactionof theenzyme. The drying is carried out on a Rapid-Kothen sheet drier.

The viscosity of the thus treated cellulose is then determined. Theresults are tabulated below:

Again it is found, as in the case of beech, that the cellulose structureis first loosened by heating, if at first strongly broken down, and ismore slowly further broken down upon prolonged reaction time.

As indicated above, the concentration of the enzyme may be varied withinvery wide limits, starting with an enzyme'obtained from a fungus such asAspergillus orzyae on a suitable nutrient medium, for example on wheatbran, which is cultivated until the fungus mycellium is completelydeveloped, the mycellium is dispersed in ten times the amount of waterso that 100 g. of said mycellium is dispersed in 1 liter of water. Thisis used as the standard of measure. This dispersion is filtered and forexample 250 cc. of this filtrate may be used on 10 g. of cellulose. Asmuch as 500 cc. of the filtrate may be used on 10 g. of cellulose, andas little as 32.66 cc. of'cellulose may be used in 10 g. of cellulose.Most preferably about -250 cc. of the solution is used on 10 g. ofcellulose.

The digestion of the cellulose is carried out in accordance with thepresent invention until the polymerization degree of the cellulose whichis converted to viscose in accordance with the present invention isbetween 400- 690. The average degree of polymerization at the lower endof the scale will generally be between 400-450 while the average degreeof polymerization at the upper end of the scale will generally bebetween 650 and 690. Most preferably the degree of polymerization of thecellulose which has been digested by enzyme in accordance with thepresent invention is preferably between 500 and 600.

Cellulose with the above degree of polymerization, such cellulose beingobtained by splitting of the longer molecular chains by the cellulose,is particularly suitable for the production of viscose in accordancewith the present invention. A peculiarity of the enzymatically digestedcellulose is that upon drying it very easily becomes horny. It istherefore advisable to work up the cellulose in wet condition. Thecellulose can be converted to dry condition while maintaining itsreaction capabilities by displacing the water with suitable organicliquids.

The use of enzymatically digested cellulose in the production of viscoseis particularly advantageous when the viscose is produced according tothe so-called singlevat process in which thecellulose to be dissolved isconverted to the final viscose in a single reaction vessel. The

carrying out of the single-vat process prior to the present inventionsuffered from the disadvantage that it was not possible to obtaincellulose with certainty within the de sired polymerization degree inthe relatively short time needed for technical purposes. The insertionof the normal ageing step for the soda cellulose is not possible in thesingle-vat method, since it is not advisable to take the reaction vesselout of use for several days in order to obtain the necessarydepolymerization of the cellulose. The addition of depolymerizationaccelerating chemicals, sulfates and the like in order to obtain a morerapid ageing to the desired degree of polymerization, aside from theprice of such chemicals, involves great difliculties in trying to usethe chemicals in such manner that the quality of the resulting viscoseis always maintained at an even level. For this reason, the use ofenzymatically partially decomposed cellulose in the production ofviscose by the single-vat method is particularly advantageous.

In any event, whether they are carried out in a single reaction vessel,or in several reaction vessels, the production of viscose in accordancewith the present invention provides for the highly advantageouselimination of the ageing step for the depolymerization of the celluloseto the desired degree of polymerization, and accordingly represents aconsiderable saving in time in the production of the viscose startingfrom the original raw material. The reduction in time is considerable,since in accordance with the present invention the partial decompositionof the cellulose by means of the enzyme requires as little as one houror less as compared to two to three days of ageing according to theknown processes.

Thus, in accordance with the present invention the entire method ofproducing viscose only involves the following stages:

The starting source of cellulose, for example timber, after removing ofthe bark, is chipped into small pieces. The chips are mechanicallymilled, and as desired, subjected to chemical treatment with calciumbisulfite or the like. These chips are then subjected to enzymaticdigestion as described above until the degree of polymerization of thecellulose is between 400 and 690, and preferably between about 500 and600.

The partially decomposed cellulose is then steeped in caustic sodasolution of about 17.5% for several hours, e.g. 1 to 4 hours. About 8%of the original pulp dissolves. The cellulose itself is swollen but notdissolved. This results in the formation of soda-cellulose.

The excess alkali is pressed out by a hydraulic ram, the pressingleaving a moist mass of soda cellulose which passes straight into ashredding machine. The shredding machine breaks up the soda celluloseinto fine crumbs.

The soda cellulose is then, without intermediate ageing, directlyxanthated by treatment with about 10% of their weight of carbondisulfide. The crumbs and disulfide are churned together producing adeep orange, gelatinous mass of sodium cellulose xanthate.

After the churning the sodium cellulose xanthate is passed into mixerswherein the sodium cellulose xanthate is stirred with dilute causticsoda solution for 4 to 5 hours while cooling the vessel. The xanthatedissolves to a clear-brown viscous liquid known as viscose. Thiscontains about 7% alkali and about 8% cellulose. The viscose istransferred to a secondary mixer or blender which generally takescharges from about eight primary mixers. In a secondary mixer or blenderthe viscose is stirred and pumped round. Since it still contains someundissolved fibers from the original wood pulp, fibers which haveresisted all of the chemical treatments, it is filtered. The firstfiltration is generally carried out through cotton-wool, and the viscoseis then twice filtered through cotton filter-cloth.

The viscose solution is then stored for 4 to 5 days generally at atemperature of 10-l8 C. and during storage'it rip-ens. During theripening the viscosity at first falls, and then rises, so that by thetime the solution is ready to spin, the viscosity has risen almost toits original value. The ripening permits the viscose to be spunsatisfactorily.

When the viscose solution is ripe, it is forced by compressed air to thespinning frames and there distributed and spun into fibers.

As is clear from the-above description, the omission of the ageing stageof the production of the viscose results in a considerable saving intime, and therefore in considerable saving in money in the overallprocess of producing viscose.

The following examples are given to further illustrate the presentinvention. The scope of the invention is not, however, meant to belimited to the specific details of the examples.

400 g. of air-dried beech textile cellulose is milled in a stonehollander at room temperature about 7 /2 hours until the milling degreeof the cellulose corresponds to about 67 Schopper-Riegler. The milledsubstance is mixed in a vat provided with a stirrer with an enzymesolution which is obtained as follows:

A strain of Aspergillus oryzae is cultivated on wheat bran and cellulosenutrient medium until formation of a thick mass of mold-fungus. Thisculture is then mixed for about one half hour in a suitable mixingapparatus with ten times its volume (measured with respect to the drynutrient medium) of tap water, intensively worked up, and then byfiltration 13 m. of extract are obtained. The biostatic strength of theenzyme solution, which has a direct relation to the cellulose-splittingactivity, amounts to 35.2. The consistency of the pulp which is mixedwith the fungus extract in the vat amounts to 3% cellulose. The reactiontemperature is maintained at 22 C.

After a reaction time of 10 /2 hours the viscosity of the cellulosewhich was originally 22 cp., was lowered to 13.7 op. The final viscosityof the digested cellulose can be adjusted by variation of the time andstrength of the enzyme solution so as to obtain a viscosity of anydesired degree.

The cellulose is then filtered through a sieve or a revolving filter toa dry content of about 40% and then subjected to the production ofviscose in the usual manner, except for the elimination of the ageingstep.

In the following tests the above enzymatically digested cellulose isconverted to viscose according to the classical viscose process, andalso according to the so-called singlevat process. After the productionof the viscose the. same is subsequently spun to fibers.

(a) Single Vat Process.The enzymatically digested cellulose is, whilestill wet, treated with caustic soda solution of 17.5% strength toproduce soda-cellulose. This soda-cellulose is then directly, withoutageing, treated for 40 minutes with 38%' carbon disulfide. TheCuoxam-viscosity of the starting cellulose amounted to 6.5 cp. Theanalysis of the finished viscose (I) showed the following values:

Viscose analysis Viscosity Filtration falling ball Ripeness, value NaOHCell. S, Permethod SR cent 9 (H) for comparison purposes. The values areindicated in the following tables: g AVERAGE VALUES The data concerningthe fibers from the enzymatically digested cellulose after 40 minutes ofxanthation compared to that of the normally aged and normal celluloseworked up to viscose in the usual manner, particularly the dataconcerning the strength surprisingly gives rise to only one conclusion.The viscose produced according to the present invention is at leastequivalent to normally produced viscose. This is particularly remarkablesince the operation in a single vat in accordance with the presentinvention omits pressing out of the caustic soda and correspondinglythere is no loss of hemi-cellulose.

(b) Usual steeping alkalizing with pressing.The enzymatically digestedcellulose is mashed in the usual manner with a corresponding excess oflye and pressed after one hour of immersion. A pressing factor of 3.35is obtained The xanthation followed without prior ageing of the sodacellulose as described above during 40 minutes with 38% carbondisulfide. The subsequent dissolving of the viscose took place in thesame manner in the blender. Again 12 spinning tests were carried outwith various times of duration in the bath, various stretching ratiosand various speeds of spinning. The values all lay in a limited region.These values are set forth in the following table.

The above table shows that with satisfactory stretching the strengthfactors are satisfactory as compared to viscose produced from normalair-ripened cellulose. In addition, the relative wet strength issomewhat increased. The filter ability of the viscose produced-inaccordance with the present invention is highly satisfactory.

The above tests actually prove that the viscose fibers produced fromenzymatically digested cellulose in accordance with the presentinvention actually have better qualities than fibers produced in thenormal manner.

The degree of polymerization of the finished fiber was about 385. Thedetermination of the degree of polymerization by means of the Cuoxammethod shows that upon further treatment to produce the viscose fibersno further lowering of the degree of polymerization occurs.

Without further analysis, the foregoing will so fully reveal the gist ofthepresent invention that others can by applying current knowledgereadily adapt it for various applications without omitting features,that from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic ,or specific aspects of this inven tionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is: vI

1. In a method of producing viscose, the improvement which comprisesconverting enzymatically digested cellulose of substantiallyequimolecular chain length having a degree of polymerization of between,about 400 and 690 to viscose. v

2. In a method of producing viscose, the improvement which comprisesconverting enzymatically digested cellulose of substantiallyequimolecular chain length having a degree of polymerization of betweenabout 500 and 600 to viscose.

3. A method of producing viscose, comprising the steps of convertingenzymatically digested cellulose of substantially equimolecular chainlength having a degree of polymerization of between about 400 and 690 tosoda cellulose; xanthating said soda cellulose without intermediateageing thereof; and converting the thus formed cellulose xanthate toviscose.

4. A method of producing viscose, comprising the steps of treatingenzymatically digested cellulose of substantially equimolecular chainlength having a degree of polymerization of between about 400 and 690with strong caustic soda solutions to as to convert said enzymaticallydigested cellulose to soda cellulose; treating said soda cellulosewithout intermediate ageing thereof with carbon disulfide so as toconvert said soda cellulose to sodium cellulose xanthate; and dissolvingsaid sodium cellulose xanthate in an aqueous liquid, thereby convertingthe same to viscose.

5. A method of producing viscose, comprising the steps of treatingenzymatically digested cellulose of substantially equimolecular chainlength having a degree of polymerization of between about 500 and 600with strong caustic soda solution so as to convert said enzymaticallydigested cellulose to soda cellulose; treating said soda cellulosewithout intermediate ageing thereof with carbon disulfide so as toconvert said soda cellulose to sodium cellulose xanthate; and dissolvingsaid sodium cellulose xanthate in an aqueous liquid, thereby convertingthe same to viscose.

6. A method of producing viscose by a single vat procedure, comprisingthe steps of treating enzymatically digested cellulose of substantiallyequimolecular chain length having a degree of polymerization of betweenabout 400 and 690 with strong caustic soda solution in a vat so as toconvert said enzymatically digested cellulose to soda cellulose;treating said soda cellulose in said vat without pressing and withoutintermediate ageing thereof with carbon disulfide so as to convert saidsoda cellulose to sodium cellulose xanthate; and dissolving said sodiumcellulose xanthate in an aqueous liquid, thereby converting the same toviscose.

7. A method of producing viscose by a single vat procedure, comprisingthe steps of treating enzymatically digested cellulose of substantiallyequimolecular chain length having a degree of polymerization of betweenabout 500 and 600 with strong caustic soda solution in a vat so as toconvert said enzymatically digested cellulose to soda cellulose;treating said soda cellulose in said vat without pressing and withoutintermediate ageing thereof with carbon disulfide so as to convert s-aidsoda cellulose to sodium cellulose xanthate; and dissolving said sodiumcellulose xanthate in an aqueous liquid, thereby convcrting the same toviscose,

8. A method of producing viscose, comprising the steps of subjectingcellulose to enzymatic digestion until the degree of polymerization ofsaid cellulose is between about 400 and 690, thereby obtaining digestedcellulose the molecular size of which is substantially equalized;treating the thus enzymatically digested cellulose of substantiallyequimolecular chain length with strong caustic soda solution so as toconvert said enzymatically digested cellulose to soda cellulose;treating said soda cellulose without intermediate ageing-thereof withcarbon disulfide so as to convert said soda cellulose to sodiumcellulose Xanthate; and dissolving said sodium cellulose xanthate in anaqueous liquid, thereby converting the same to viscose.

9. A method of producing viscose, comprising the steps of subjectingcellulose to enzymatic digestion until the degree of polymerization ofsaid cellulose is between about 560 and 600, thereby obtaining digestedcellulose the molecular size of which is substantially equalized;treating the thus enzymatically digested cellulose of substantiallyequimolecular chain length with strong caustic soda solution so as toconvert said enzymatically digested cellulose to soda cellulose;treating said soda cellulose without intermediate ageing't hereof withcarbon disulfide so as to convert said soda cellulose to sodiumcellulose xanthate; and dissolving said sodium cellulose xanthate in anaqueous liquid, thereby converting the same to viscose.

References Cited in the file of this patent UNITED STATES PATENTS2,028,846 Richter Jan. 28, 1936 OTHER REFERENCES Henningsen July 25,1933

1. IN A METHOD OF PRODUCING VISCOSE, THE IMPROVEMENT WHICH COMPRISESCONVERTING ENZYMATICALLY DIGESTED CELLULOSE OF SUBSTANTIALLYEQUIMOLECULAR CHAIN LENGTH HAVING A DEGREE OF POLYMERIZATION OF BETWEENABOUT 400 AND 690 TO VISCOSE.